1. Field of the Invention
The present invention relates to a polishing pad of a chemical mechanical polishing (CMP) apparatus and to a method of manufacturing the same.
2. Description of the Related Art
In a typical polishing process performed by a chemical mechanical polishing (CMP) apparatus, a surface of an object is polished by pressing the surface of the object against a rapidly rotating polishing pad and providing slurry between the polishing pad and the surface of the object. The slurry includes an abrasive such as silica (SiO2) or ceria (CeO2), and chemical additives such as surfactants. Therefore, the entire surface of the object is polished by friction created between the abrasive and the surface of the object as well as by a chemical reaction that occurs between the slurry and the object.
In the manufacturing of semiconductor devices and the like, CMP is often used to polish a substrate on which a fine pattern has been formed by a photolithographic process. In particular, the CMP process is used to create a level surface after the fine pattern has been formed and has thereby created steps at the surface of the substrate. However, the CMP process may seriously affect the fine pattern if the process is not controlled precisely. This problem is of great concern in the manufacturing of highly integrated semiconductor devices.
In particular, the pressure between the polishing pad and the substrate is typically adjusted during the CMP process to ensure that the surface of the substrate is polished uniformly. However, in a conventional CMP process, the pressure between the polishing pad and the substrate may depend on the surface of the object being polished. Therefore, the technique of controlling the pressure between the polishing pad and the substrate is difficult to use in a manufacturing process in which CMP is used to polish various surfaces, such as that of a bare substrate, a metal layer, an oxide layer, a nitride layer, and an oxynitride layer, etc. Thus, the polishing pad of a current CMP apparatus has a plurality of grooves in front and rear surfaces thereof in an attempt to ensure that surfaces of the objects, e.g., surfaces on the semiconductor substrates, are all polished uniformly.
FIG. 1 illustrates such a conventional polishing pad of a CMP apparatus. Referring to FIG. 1, the conventional polishing pad 3 is disposed on an upper portion of a plate 1. The polishing pad 3 has grooves 5 and 7 in front and rear surfaces thereof, respectively. The grooves 5 and 7 may improve the uniformity at which surfaces of an object are polished using the polishing pad 3 as compared to a corresponding polishing pad without the grooves. However, the grooves 5 and 7 still can not ensure that all of the different surfaces will be polished uniformly. Additionally, the grooves 5 and 7 reduce the useful life of the polishing pad 3 because the portions of the polishing pad provided with the grooves 5 and 7 are prone to being damaged during the polishing process.
FIG. 3 is a graph of ideal rates at which a central portion and edge portions (representing the periphery) of a surface of an object should be polished using the polishing pad shown in FIG. 1. The graph applies to various surfaces that might be polished such as the surface of a bare semiconductor substrate, an oxide layer, a nitride layer, an oxynitride layer, a metal layer or a metal oxide layer. In FIG. 3, reference character A denotes a tolerable difference between the ideal rate at which the central portion of the object should be polished and the ideal rate at which the edge portions of the object should be polished. That is, as shown in FIG. 3, the central portion of the object may be ideally polished at a rate substantially the same as or slightly higher than the rate at which the edge portions of the object are polished.
FIG. 4 is a graph illustrating actual rates at which various regions of a metal layer on a substrate are polished using the polishing pad shown in FIG. 1. Referring to FIG. 4, the central portion of the object is polished at a rate substantially higher than the rate at which the edge portions of the object are polished. That is, the central portion of the metal layer is removed faster than the edge portions of the metal layer in a CMP process carried out using the CMP apparatus shown in FIG. 1.
FIG. 5 is a graph illustrating actual rates at which various regions of an oxide layer on a substrate polished using the polishing pad shown in FIG. 1. As shown in FIG. 5, the rate at which the edge portions of the oxide layer are polished is substantially greater than the rate at which the central portion of the oxide layer is polished. That is, the edge portions of the oxide layer are removed faster than the central portion of the oxide layer in a CMP process performed using the CMP apparatus shown in FIG. 1.
FIGS. 2A to 2C illustrate a method of manufacturing the conventional polishing pad of a CMP apparatus.
Referring to FIG. 2A, the material of the pad is extruded into a mold 9 by an extruder 11, and the extruded material is hardened in the mold 9. The hardened material is extracted from the mold as an intermediate product having the form of a disc 13 as shown in FIG. 2B. Then, the disc structure 13 is sliced to produce several polishing pads 13a, 13b and 13c as shown in FIG. 2C. Therefore, the polishing characteristics of the polishing pads 13a, 13b and 13c are all the same. That is, the polishing pads 13a, 13b and 13c can not be used in a manufacturing process in which different types of surfaces, such as that of a bare substrate, an oxide layer, a metal layer, a nitride layer and/or an oxynitride layer, must all be polished uniformly by CMP.